1. Field of the Invention
The present invention relates to synchronizing multiple disk drives.
2. Background Art
Disk drives store data on rotating storage elements such as magnetic or optical disks. An array of disk drives may be used to increase data throughput, decrease access latency, provide fault tolerance, and the like. A common disk array system for distributing data amongst several disks is referred to as a Redundant Array of Independent Drives (RAID). In a typical RAID system, a single logical storage device is created using multiple physical devices, such as magnetic disk hard drives. There are many RAID techniques (known as “levels”) with varying design goals and performance profiles. Some of the most common are RAID levels 1, 5, 10, and 0+1. In such RAID systems, a single block of data is distributed across multiple physical drives. The failure of any single disk causes no data loss due to redundant storage.
In order to increase performance, data may be written to multiple disks in different disk drives roughly simultaneously. However, as disks in different drives tend to be in different relative rotational positions, the latency before accessing data may be different for each drive. Various solutions for synchronizing the disks in different disk drives have been proposed. Typically, a master disk drive generates a synchronization signal that is distributed to the remaining slave drives. All these solutions require special wiring for distributing the synchronization signaling. This increases the cost of such systems and makes installation into existing disk arrays difficult.